Wireless systems have been widely adopted for various applications and networks. The applications include medical instruments and equipment, wireless consumer products, wireless equipment used in stores, automotive equipment, control systems, security systems, etc. The networks include personal and commercial communication networks, global positioning system (GPS) networks, cellular networks, broadcasting networks, industrial control networks, wireless local area networks (WLANs), etc. Examples of WLANs are Wi-Fi™ networks, Bluetooth® networks, automobile control and sensor networks, and home and office automation and security networks (e.g., a ZigBee™ network).
Zigbee protocols for wireless communication are being used for the “Internet of things” to provide connectivity and control to various items (e.g., appliances, equipment, sensors, computers, and cellular devices) in a wireless network. Zigbee is a wireless mesh network standard for low-cost and low-power network devices. ZigBee defines a protocol stack that is based on physical layer (PHY) and medium access control (MAC) layer protocols defined in the Institute of Electrical and Electronics Engineers (IEEE) 802.15.4 standard. The protocol stack includes: a network layer that communicates with the MAC layer; a security layer; and an application programming interface (API). The network layer performs address assignment, route discovery, and connection establishment. The network layer supports star, mesh and cluster-tree networks. The security layer provides 32-bit, 64-bit, or 128-bit encryption. The API is in communication with an application layer. The application layer includes application objects, a profile and software associated with a network (or customer) device.
According to IEEE 802.15.4, the PHY layer transmits in an 868 mega-hertz (MHz) band, a 915 MHz band, or a 2.4 giga-hertz (GHz) band. The 868 MHz band includes frequencies 869.0-868.6 MHz and is used in Europe. The 915 MHz band includes frequencies 902-928 MHz and is used in the United States of America. The 2.4 GHz band includes frequencies 2.405-2.480 GHz and is used worldwide.
The IEEE 802.15.4 standard specifies a mandatory mode of operation for the 2.4 GHz band. The mandatory mode of operation includes transmitting data at a data rate of 250 kilo-bits-per-second (kbps). The 2.4 GHz band includes 16 channels. Consecutive ones of the 16 channels are 5 MHz apart from each other. FIG. 1 shows a format of a frame 10 according to IEEE 802.15.4. The frame 10 includes a synchronization header (SHR), a PHY header (PHR), and a PHY payload. The SHR includes a preamble and a start-of-frame delimiter (SFD). The preamble of the frame 10 is used by a receiver to obtain chip and symbol synchronization with an incoming message. The preamble includes 4 bytes (or octets). The 4 bytes include 32 binary zeros. The SFD includes a single byte and indicates an end of the preamble and a start of packet data. The PHR includes a frame length field and a reserved bit. The frame length field includes 7 bits and indicates a total number of bytes of data in the PHY payload. The PHY payload is a PHY service data unit and may include up to 127 bytes of data.